JPS60134548A - Loudspeaker telephone set - Google Patents

Abstract

PURPOSE:To prevnt the head of speech from being missed by providing a switch decreasing the gain of a transmission/reception circuit to a desired gain and also fixing the attenuation of the transmission/reception circuit to a small value at a short distance talking to bring about the simultaneous transmission/reception state with the operation of the switch. CONSTITUTION:Trunk lines L1, L2 are connected to a voice amplifier 2 via a hybrid circuit 1, and after a voice signal is amplified at reception, its output is fed to a variable attenuator 15 and a switch control circuit 14. The output of the attenuator 15 is fed to an output amplifier 12 provided with gain adjuster and its output drives a speaker 5. Moreover, an output of microphone 6 is amplified by a voice amplifier 13 provided with gain adjuster, its output is fed to the circuit 4 and the variable attenuator 16, and an output of he attenuator 16 is transmitted to the trunk lines L1, L2 via a voice amplifier 9 and the circuit 1. A talking mode changeover switch 11 is provied between the amplifiers 12 and 13, the gain of the amplifiers 12, 13 is brought into a desired value by controlling the circuit 14 to control switches S1, S2 of the attenuators 15, 16 thereby fixing the attenuation to a prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an improvement in a loudspeaker telephone device that allows telephone calls to be made through a microphone and speaker without having to raise the handset of the telephone.

PRIOR ART AND PROBLEMS A loudspeaker telephone device is a device that allows a person to talk to the other party without having to pick up the handset ( ) or handset of the telephone set. Depends on what is used. In such loudspeaker telephone devices, those using a point switch have been commonly used in order to automatically switch between transmitting and receiving operations.

FIG. 1 shows the configuration of a conventional voice switch type loudspeaker telephone device. In the figure, 1 is a hybrid circuit using a DC cutoff transformer, H is a balanced circuit network, 2 is an audio amplifier (reception amplifier), 5 is a reception variable attenuator, 4 is an output amplifier (power amplifier), is the speaker,
6 is a microphone, 7 is an audio amplifier (mic amplifier),
8 is a transmitting variable attenuator, 9 is an output amplifier (transmitting amplifier),
10 is a comparator.

In FIG. 1, the 1st station line L1. L2 is connected to the audio amplifier 2 via the hybrid circuit 1, with direct current cut off. During reception, the audio amplifier 2 amplifies the received audio signal, and its output passes through the variable attenuator 3 and is amplified by the output amplifier 4 to a level sufficient to drive the speaker 5.
This causes the speaker 5 to emit the received audio.

On the other hand, during transmission, the audio signal from microphone B is amplified by the audio amplifier 7, passes through the variable attenuator 7, and is further amplified to the level of the line signal by the output amplifier 9, and is output.

Comparator 10 compares the outputs of both audio amplifiers 2.7, and when receiving a signal with a large output from audio amplifier 2, it reduces the attenuation of variable attenuator 6 and increases the attenuation of variable attenuator 8.

As a result, the central line L1. The audio signal from L2 is emitted from the speaker 5, but the audio signal from the microphone 6 is greatly attenuated by the variable attenuator 8. On the other hand, when the output of the audio amplifier 7 is large during transmission, the attenuation of the variable attenuator 3 is increased and the attenuation of the variable attenuator 8 is decreased. As a result, the audio signal from microphone 6 is transferred to central line L1. Sent to L2.

In the loudspeaker telephone device shown in FIG. 1, the attenuation of the variable attenuator 6 is reduced and the attenuation of the variable attenuator 8 is increased during reception, and the attenuation of the variable attenuator 8 is reduced during transmission. Control to increase the attenuation of the variable attenuator 6 is performed by comparing the signal levels of both the audio amplifiers 2 and 7 in the comparator 10. As a result, the sound emitted from the speaker 5 is inputted from the microphone 6, passes through the hybrid circuit 1, etc., and goes around the speaker 5 again, causing howling.
'CD, this prevents howling from interfering with the other party's receiving signal and interfering with telephone calls.

However, in the loudspeaker telephone device shown in FIG. 1, the operation of the voice switch as described above based on the detection result of the comparator 10 causes problems peculiar to the loudspeaker telephone device, such as an intermittent feeling at the time of switching and a disconnection at the beginning of one episode.

In other words, normally a voice switch needs to be designed to satisfy the transmission and reception level even in the case of the worst line loss due to long distance operation.Therefore, the gain of the transmission and reception circuit must be sufficiently high, and it must be designed to prevent hacking. Therefore, the loss amount of each variable attenuator must also be increased. However, if the variable loss amount is large, the voice from the other party cannot be heard during transmission, resulting in a one-way conversation, giving an unnatural feeling and causing a sense of discontinuity when switching.

In addition, due to the large gain of the transmitter/receiver circuit and the large variable loss amount of the attenuator, the start-up time is delayed, resulting in a disconnection at the beginning of the speech.

On the other hand, when the loudspeaker telephone equipment is used at a short distance such as within the same premises, the gain of the transmitting/receiving circuit does not need to be increased, and therefore the amount of attenuation of the variable attenuator can be small. Since the amount of variable attenuation and variable attenuation are constant, it must always be used in the same state as in the case of long distances as described above.

OBJECT OF THE INVENTION The present invention is intended to solve the problems of the prior art as described above6.The purpose of the present invention is to provide a public address telephone device configured to prevent howling by using a voice switch. An object of the present invention is to provide a loudspeaker telephone device that enables simultaneous transmission and reception when making a call, thereby alleviating problems peculiar to the loudspeaker telephone device, such as a sense of discontinuity during switching and disconnection at the beginning of a conversation. .

Structure of the Invention The loudspeaker telephone device of the present invention uses a voice switch method to compare the received signal level and the transmitted signal level, and when the received signal level is high, reduces the attenuation of the receiving circuit and increases the attenuation of the transmitting circuit. In a public address telephone system that prevents howling by reducing the attenuation of the transmitting circuit and increasing the attenuation of the receiving circuit when the transmitted signal level is high, the transmitting circuit and the receiving circuit can be The gain of the circuit is lowered to a required gain, and the attenuation of the transmitting circuit and receiving circuit is fixed to a small state.

Embodiment of the Invention FIGS. 2A and 2E show the configuration of an embodiment of the loudspeaker telephone device of the present invention. In the same figure, the same parts as in FIG. The switching control circuits 15 and 16 including comparators are variable attenuators, respectively. Also S
+r 82 are switches provided in the variable attenuators 15 and 16, for example, FET switches or 0M
An O8 (IC) analog switch or the like is used to switch between high resistance and low resistance. FIG. 2A shows the circuit state in the case of a long distance, and FIG. 2B shows the circuit state in the case of a short distance.

When using the loudspeaker telephone device at a long distance, the call mode selector switch 11 is turned off as shown in FIG. 2A. In this state, each amplifier 12, 13 is placed in a high gain state corresponding to the worst case of line loss. Switching control circuit 1
4, when the output of the audio amplifier 2 is large, the switch S+ is turned on and the switch S2 is turned off, thereby controlling the attenuation of the variable attenuator 15 to be reduced and the attenuation of the variable attenuator 16 to be increased. As a result, the central line L1. The audio signal from L2 is emitted from the speaker 5, but the audio signal from the microphone 6 is greatly attenuated by the variable attenuator 16 (FIG. 2A shows this state).

When the output of the audio amplifier 16 is high during transmission, the switch S2' is turned on and the switch 81' is turned off (switches S1*82 in FIG. 2A are switched to the dashed line side), and the variable The attenuation of the attenuator 16 is decreased and the attenuation of the variable attenuator 15 is increased.

As a result, the audio signal from the microphone 6 is transmitted to the central office line L1.
．． It is sent to Z,2. That is, the operation in the case of a long distance is the same as that of the conventional circuit shown in FIG.

On the other hand, when using the phone at a short distance, turn on the call mode changeover switch 11 as shown in FIG. 2B.

In this state, each amplifier 12, 13 is lowered to a required gain that does not generate howling, and the switching control circuit 14
In this state, both switches S I t 82 are turned on. Therefore, both variable attenuators 15 and 16 are in a state where attenuation is small. As a result, the central line L1.
At the same time that the audio signal from L2 is emitted from the speaker 5, the audio signal from the microphone 6 is transmitted to the central office line L1. The signal is sent to L2 and a state is established in which simultaneous transmission and reception are performed. In this case, even if the sound from the speaker 5 returns to the microphone B and there is a feedback condition or the like, no /1 ringing will occur because the gains of the amplifiers 11 and 12 are low.

FIG. 6 shows a switching control circuit (second
14) in Figures A and E - shows a specific configuration diagram as an example,
FIG. 4 shows the output amplifier 12 with a gain adjuster and the audio amplifier 16 shown in FIG.
1 shows a specific configuration diagram as an example of No. 1.

In FIG. 3, the switching control circuit 14 includes a comparator 142 that compares all the outputs of the audio amplifier 2 and the audio amplifier 16 with a gain adjuster, an inverter 141 that inverts the signal of one of the outputs of the comparator 142, and The circuit configuration is such that the operation of the comparator 142 and inverter 141 is disabled by an ON signal (logic signal level "1") from the call mode changeover switch 11. When the call mode selector switch 11 is turned OFF, that is, when used for long-distance use, each variable attenuator 15 is Exclusively control ゜16, switch S++Sz
'(!: Turns on and off when sending and receiving calls.

On the other hand, in the case of use at a short distance, by turning on the call mode selector switch 11, the switch S of the variable attenuator 15 and 16 can be set to
l+82'jc is turned on to reduce the amount of loss.

Further, in the case of use at a short distance, gain adjustment of the amplifiers 12 and 13 by turning on the call mode selector switch 11 will be explained with reference to FIG.

In FIG. 4, in the amplifier i2.13 with a gain adjuster, gain adjusters GC and GC' are connected in parallel to amplifiers 121 and 131, respectively, and the gain adjusters GC and GC' are connected to the resistor R11"'2 + RA and R+' l R2' +
R3', field effect transistor FET1, FE
Each consists of T1.

Here, when the call mode selector switch is on, FET1+P
ET 1' is in a low resistance state and amplifier 121.131
The gain of is reduced to the gain determined by the parallel resistance values of RI + R2 and E,', R2'.

When the call mode selector switch 11 is off, the FET
1. Since no voltage is applied between the gate and source of FET 1', a high resistance state and no amplifier 121°16
The gain of 1 is determined by the resistance E+rR,'.

The above operations can be summarized as follows.

(b) In the case of long distances, the call mode selector switch is turned off, so the variable attenuator operates by comparing all the transmitting and receiving levels, and performs contradictory operations depending on the comparison results.

Also, at this time, since the gain adjuster does not operate, both amplifiers are in a high gain state.

(b) In the case of short distances, when the call mode selector switch is turned on, the variable attenuator
Since a signal of 1°' is sent, both are in the ON state (heat loss).

Furthermore, since the gain adjuster operates at the same time, the gain of the amplifier output decreases.

Note that the gain to be reduced is reduced by the amount that the variable attenuator is turned on and the loose gain is increased, so that the loop gain does not vary depending on the call mode.

In this way, in the loudspeaker telephone apparatus of the present invention shown in FIGS. 2A and 2H, when used at short distances, the gain of the transmitting and receiving circuits is low and a large amount of attenuation is not inserted in each, so that simultaneous transmitting and receiving is possible. This makes it possible to reduce the problems peculiar to loudspeaker telephone devices, such as an unnatural sense of discontinuity at the time of switching and disconnections at the beginning of speech.

As described in detail, the loudspeaker telephone device of the present invention reduces the gain of the transmitting circuit and the receiving circuit to the required gain and fixes the attenuation of the transmitting circuit and the receiving circuit to a small state during short-distance calls. By operating this switch, it is possible to simultaneously transmit and receive calls during short-distance calls.This eliminates the unnatural sense of interruption when switching between transmitting and receiving, and also eliminates the disconnection at the beginning of a conversation. This has the effect of making the public address telephone device easier to use.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the structure of a conventional loudspeaker telephone system.
Figures A and E are diagrams showing the configuration of an embodiment of the loudspeaker telephone device of the present invention, Figure 3 is an example of the configuration of the switching control circuit shown in Figures 2A and B, and Figure 4 is the configuration of the switching control circuit shown in Figures 2A and 2B. B is a diagram showing an example of the configuration of the amplifier with a gain adjuster shown in FIG. 1...Hybrid circuit, 2...Audio amplifier...3
...Variable attenuator, 4...Output amplifier, 5...Speaker, 6°°゛microphone, 7...Audio amplifier, 8
... Variable attenuator, 9... Audio amplifier, 10... Comparator, 11... Call mode changeover switch, 12...
Output amplifier with gain adjuster, 13-pass audio amplifier with gain adjuster, 14... switching control circuit, 15.16° variable attenuator Patent applicant Fujitsu Ltd.

Claims (1)

[Claims] Comparison control means for comparing the reception signal level of the reception circuit and the transmission signal level of the transmission circuit and reciprocally controlling the attenuation of each of the signal levels, and the comparison control means being disabled, the transmission circuit and the reception circuit 1. A loudspeaker telephone device, characterized in that it is completely equipped with switching means for fixing the attenuation of the signal to a small state and lowering the gain of the transmitting circuit and the receiving circuit to a desired gain.